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GC SLS

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aacilla's version from 2017-08-15 04:55

Midstance

Question Answer
What percentage of the GC does Midstance make up?12-31%
What are the objectives of this phase?Progression over the stationary foot and limb/trunk stability
What phase is the contralaterl leg in?Midswing
What is the ankle position during mid stance?10ºPF to 5ºDF,
What is controlling ankle position during mid stance?gastroc-soleus eccentrically control forward tibial progression
What is the position of the sub-talar joint in mid stance?Calcaneus is everted about 5 degrees, mid-tarsal is unlocked and foot is pronated.
What is the reason behind foot pronation in mid stance?Shock absorption
What muscle is firing eccentrically to control the pronation of the foot in mid stance?The posterior tibialis in order to internally rotate the tibia.
What is the FIRST thing to happen to the knee during midstance? (What muscle is firing to put knee in its specific position?)The quads are CONCENTRICALLY firing to assist the knee to move into about neutral.
What assists the move of the knee into neutral during midstance? (HINT it's not a specific muscle)The forward momentum of the contralateral swing limb.
What is the SECOND thing to happen to the knee during midstance, which enables it to stay extended?The ground force reaction moves anteriorly to the knee, which keeps it extended, and allows the quads to stop firing.
What is the stabilizer of the knee during midstance after is is extended?The gastroc soleus complex eccentrically controls it.
Where are ground reaction forces at the end of mistance?anterior to the knee and posterior to the hip!
True or false, muscle activity is required at the knee and the hip at the end of mid stance.False-the ground force reaction is naturally controlling them.
What is the position of the hip during midstanceHip extension 25-0º
What is the position of the knee during midstance?Knee flexion 15-5º
What is controlling hip position at midstance?Ground force reaction (No glut max or hamstring firing once the GRF falls posteriorly to hip joint.)
What is the position of the pelvis during mid stance?Backward rotation to neutral.
memorize

Midstance GRF

Question Answer
GRF at hippasses through hip=no moment
GRF at kneeposterior knee=external KF=internal/eccentric KE
GRF at ankleanterior=external DF=internal/eccentric PF
Hip muscle activityhip abductors continue to minimize pelvic drop
Knee muscle activityQuads (ecc) resist KF until COG passes over BOS, then quads are silent
Ankle muscle activityTriceps surae (ecc) control forward tibial progression
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Terminal Stance

Question Answer
What percentage of the GC does this phase make up?31-50%
What is the objective?Progression of body beyond the supporting foot
What is the ankle position during terminal stance?Heel rises, dorsiflexion by about 10 degrees.
What muscle is eccentrically contracting to prevent tibial collapse during dorsiflexion of the ankle in terminal stance?Gastroc-soleus complex
Where has the axis of rotation reached in late terminal stance?Metatarsal heads.
Because the axis of rotation has reached the metatarsal heads in terminal stance, what motion is the forefoot going through?Forefoot rocker
In late terminal stance the dorsiflexion of the foot (increases/decreases)?Decreases, to a halt.
In late terminal stance, which muscle switches to concentric to stabilize the ankle joint and allow the tibia and foot to roll forward on the forefoot rocker?Gastroc
What percentage of acceleration force is seen in the terminal stance?80% of acceleration force
What is the position (or increase in positioning) of the sub-talar joint in terminal stance?Gradual calcaneal inversion (supination), as the midtarsal joint locks.
What does supination of the foot provide in terminal stance in terms of for movement?A rigid lever for propulsion.
What does the tibia do during terminal stance, as it is being controlled by concentric firing of the posterior tib?Tibia is externally rotating.
Which muscles in the leg provide lateral stability to the foot and leg in terminal stance?Peroneus longus and brevis
The peroneus longus (eccentrically/concentrically) fires as the foot supinates to support the arch and keep the first ray on the ground in terminal stance?Eccentrically
What is the position of the knee in terminal stance?varus and extension 0-5º
How is the knee joint kept stabilized in terminal stance?By the gastroc-soleus complex
What is the varus motion of the knee stabilized by in terminal stance?Lateral knee and ankle ligaments
What is the position of the hip in terminal stance?Extension by about 20 degrees. Hyperextension.
Hip extension in terminal stance causese (posterior/anterior) tilt of the pelvis?Anterior
What stabilizes the hip in terminal stance?The anterior hip capsule (passive)
What is the position or the continuation of position of the pelvis in terminal stance?5 degrees of backward rotation and anterior tilt. Also, pelvis is neutral in frontal plane.
memorize

GRF Terminal Stance

Question Answer
GRF at Hipposterior=external HE=internal HF
GRF at Kneeanterior=external KE=internal KF
GRF at ankleanterior=external DF=internal PF
Muscle activity at hipbrief burst from hip flexors resisting hyperextension of hip
What muscle is now resisting pelvic dropTFL active throughout stance to resist pelvic drop
Muscle activity at kneeminimal to no quad or ham activity
memorize
Muscle activity at ankle: PF prevent forward tibial collapse and contribute to heel raise through passive tension